> Folks seem unbelievably harsh on accents they know not to be the native one, which is every time a famous actor does an accent

Either Hugh Laurie isn't famous, or you don't have any idea he's British. ;)

Every time he plays House, he's doing a fake American accent. He just does it really, amazingly well.

Here's Hugh Laurie as the Prince of Wales (the total idiot) in a short segment from the series "Blackadder the Third":

http://www.youtube.com/watch?v=hOSYiT2iG08